The Solnhofen Limestone of Germany

Towards the end of the
Jurassic, about 155 milion
years ago, a warm shallow sea studded with islands covered much of what is now
Germany. Sponges
and corals
grew on rises in this sea, forming reefs that divided up parts of this sea into
isolated lagoons. These lagoons were cut off from the ocean and also from
terrestrial runoff. Within these warm, isolated lagoons,
the salinity rose, and the water may have been anoxic (depleted of oxygen)
or even toxic at various intervals. Aside from
cyanobacteria
and small protists such as
foraminifera,
nothing could survive in the bottom waters of the lagoons
for very long. However, any organism that
fell into the lagoons from the land, or that drifted or was washed into the
lagoons from the ocean, was buried in soft carbonate muds.
Thus, many delicate creatures were not consumed by scavengers or torn apart
by currents.

Today, in the state of Bavaria, in region between Nuremberg and Munich, these
carbonate muds form a type of fine-grained, flat-cleaving
limestone (known as Plattenkalk in
German) that has been quarried since the Stone Age for roof and floor tiles,
and more recently for lithography. These rocks -- known as the Solnhofen
or Solenhofen
Limestone, after the small town of Solnhofen -- are also famous for their
fossils. Although relatively rare, fossils from the Solnhofen Limestone may
show exquisite detail, and often include fragile or soft-bodied organisms that
usually leave no fossils at all, or only fragmentary ones.
Vertebrate
and invertebrate
animals,
land plants, and
protists are all
represented as fossils in the Solnhofen Limestone.

From sites like
this with exceptional preservation, called by the German name
Lagerstatten, paleontologists have learned a great deal. Such sites
may be the only source of information on fossil organisms that would
otherwise leave no traces at all. They allow organisms of the past to be
reconstructed in great detail; for instance, the only way we know that
Archaeopteryx
had feathers is from its exceptional preservation in the Solnhofen Limestone.
They also allow more accurate reconstruction of past ecosystems by giving
an unusually complete picture of the biodiversity of their times.